Insulating 1 1/2 story 1050’s house
Hi,
I have been working on a kitchen renovation project and got into opening up the ceiling in a 1 ½ story house. Discovered problems with the insulation and venting in the rafters. Have some questions on the plan or course of action to best insulate the lower portion of the attic. Facts of the house are below.
House type: 1 ½ story, 1950 built. Pitched triangular roof
Dormer: Front side of house is comprised of 2nd floor bathroom and not centred on the roof, offset. The other side of the roof has a smaller dormer that is a flat section of roof for the landing of the stairs for the 2nd floor.
Ice dams: Both sides of the roof has ice dams.
Summer: Really hot 2nd floor bedrooms
Rafters: roof 2 x 4
Insulation: Rafter faced batts. Some batts are still attached to the roof deck, others half attached, hanging. There is also batts wrapped around 2 x 4 at the eaves, just above the top plate of the 1st floor wall. There is also fiberglass or wool batts still secured to the roof deck in the slant portion of the roof that leads to the upper/top attic. However, not sure these batts are effective in each rafter cavity.
Eaves: Closed, approx depth 4”-5” and height 4” do feel some air flow
Exterior wall: Double cinder block 4” x 8” butted against each other
Roof Sheathing: wood planks, ¾ inch depth
Vents: 2 gable at top of attic
Roof vent: At top of peak slant vent on south side and at an addition south side where bedroom was extended at top/upper attic
Upper attic: Insulation batts in joist cavity of ceiling/floor original, old fiberglass insulation blown in and recently 2yrs ago blown cellulose insulation, top up. Feels more comfortable on 2nd floor bedrooms in winter since increasing the insulation in top attic. Summer is still quite unbearable.
Planning to insulate the lower portion of the attic where my 1st floor living room is on one side of the front dormer and on the other side of the dormer is the front entrance & small bathroom.
Insulate with batts, rockwool in the joist cavity of the 1st floor ceiling, block the top plate/caulk blocking and Insulate knee wall for 2nd floor bedroom, one side of dormer & 2nd floor closet that is other side of the front dormer. Finally, cover each rafter with foam board EPS insulation R-3.75. The foam board acts as an additional barrier and to allow air flow up from each rafter/eaves to the top of the roof.
Also planning to open the ceiling on the other side, south side 1st floor. Insulate probably the same method as mentioned above.
Question: Does the plan for insulation upgrade seem correct, reasonable to reduce ice dams? And keep the house cooler on the 2nd floor in summer?
Should I create an opening in the rafter through the new fastened foam board to create some air flow into the lower portion of the attic? As I am planning to cover the rafters with the foam board from top plate at eaves to about 5-6 feet or top of knee wall/top of closet.
As well, should I insulate the bare cinder block, adjacent to the knee wall and closet wall? Essentially, I am referring to the side of the house that is above the 1st floor ceiling where I can access. My thought is yes. Air seal the cinder block wall first, then lay rockwool batts and seal/tape the joints.
Does my plan seem correct and will it work? Meaning improve/reduce the ice dams in winter and keep the 2nd floor cooler in the summer time?
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Replies
Hi Bauerspoint,
If I'm reading you post correctly, your home is a cape cod design. This style of roof is not the easiest to insulate and air seal. The best way to go about this process has been covered in an article on GBA: https://www.greenbuildingadvisor.com/article/insulating-a-cape-cod-house
Hopefully this helps in your planning.
Randy
Thank you on the link. I have a read the link and very helpful. I should have put in the posting I am zone 6 and house is 1950's.
I am little puzzled on the blocking above the knee wall in each rafter bay. By blocking each rafter 16" on centre, it prevents air flow for each rafter and flowing to the top of attic? If I were to do that, I think I would need to add roof vents on ether side of my front dormer? Like I have seen other 1 1/2 story houses in my neighbour hood. Would that be the best approach, blocking and adding roof vents approximately 4'-5' up from the eaves? Since opening up the ceiling in my living room I have suspected for quite some time of a moisture problem in this area as the ceiling has shown cracks. Now have seen moisture droplets coming through from a recent from a snow fall the roof sheathing and feeling damp in the rafters where it is above the knee wall. This so happens where the wool batts are pretty flush to the roof/sheathing.
Hi Bauerspoint,
Chances are the moisture you are seeing in the roof is from air leaks, the moisture is condensing on the cold underside of the roof deck. Air sealing the lid will help.
As far as the blocking, this is installed with the air chute already in place, the attic is still ventilated. The blocking is there to retain the insulation and limit wind washing, which can strip away the performance of the insulation.
Randy